(a) Field of the Invention
The present invention relates to the optical information recording medium, in particular relates to the optical information recording medium suitably used in writing and reading with a high density energy beam such as laser beam wherein the recording layer superimposed on the substrate has been divided into the reflective layer and the light absorptive layer.
(b) Description of the Prior Art
A great number of optical information recording mediums for use in writing and reading with a high density energy beam (for instance, laser beam) have been developed up to the present. As the typical ones there can be enumerated the recording medium prepared by providing the vapor deposition film of metal, semimetal or nonmetal on the substrate and the recording medium prepared by coating silver halide emulsion onto the substrate and heating same to thereby form the reflective layer thereon (Japanese Laid Open Patent Application No. 108995/1980).
As the recording layers (said vapor deposition films or reflective films) for use in laser recording mediums there are known (1) thin metal films with holes melt-formed by radiation of laser beam, (2) composite lustrous vapor deposited films whose reflective index is reduced at some spots by radiation of laser beam, (3) thin films of dyes or other coating agents that can be removed at some spots by radiation of laser beam and (4) dielectric substances in which the refractive index is varied at some spots by radiation of laser beam and light diffusion is caused when it is scanned by a reading laser beam.
However, the recording mediums using vapor deposited films of metal, semimetal or nonmetal, which are generally prepared by a vacuum molding method of the batch type rather than the continuous type, are defective in that they are expensive and further it is difficult to attain a uniform quality of them, when massproduced, because a number of batches are used therein. On the other hand, the process of forming the reflective layer by coating silver halide emulsion onto the substrate and heating same is troublesome in the necessity of pre-coating silver halide emulsion onto the substrate, involves the problem of carrying out the heat treatment at a temperature of 300.degree. C. or more, and further the recording medium prepared by this process is defective in that it is difficult to form the reflective layer of a uniform silver density because the silver density gradient is designed to fall from the reflective layer surface toward the substrate when viewed from the relation between the reflective layer and the light absorptive layer, and it is difficult to obtain the light absorptive layer of a uniform quality because the aforesaid tendency is also observed in the light absorptive layer.